Power line communication system and an intelligent meter

ABSTRACT

A power line communication system including a plurality of intelligent devices in communication with a power line and operable to monitor energy usage at a site and communicate usage data onto the power line, and a controller also in communication with the power line, wherein each intelligent device maintains a routing table identifying a first set of other intelligent devices downstream of it relative to the controller that it can communicate with directly and identifying a second set of other intelligent devices downstream of it relative to the controller that it can communicate with through one or more of the first set of other intelligent devices.

TECHNICAL FIELD

This invention relates to communication methodologies and systemsutilising power lines, such methodologies and systems often alsoreferred to as mains communication methods and systems. In particular,but not exclusively, the present invention relates to the establishmentof a power line communication network and a method of communicating overthe network.

BACKGROUND

Communication over power lines has been proposed and used for remotemetering. In typical systems for remote metering, a central controllercommunicates with a meter using a superimposed signal on the mainsnetwork. A meter sends an acknowledgement signal back to the centralcontroller and may perform some function dependent on the messagereceived.

Two well known problems that need to be overcome by power linecommunication systems are the noisy environment and potentially largesignal attenuation. Various reading techniques and communicationprotocols have been developed to address these problems, for exampleusing meters as digital relays to enable communication from the centralcontroller to each of the meters. Examples of power line communicationsystems using signal repeaters are described in European patentpublication No. 0 201 253 B1 and international patent publication no. WO95/01030.

Advances in meter technology have provided improved functionality. Forexample, meters may communicate by a wireless link with other meters andwith network controllers to perform various functions. An example ofsuch a system is described in international patent publication no. WO97/29466. A problem with such meters is the additional costingcomplexity resulting from the wireless communication. Also, as radiospectrum becomes increasingly in demand, the use of wirelesscommunication from potentially millions of sources may not becommercially viable in many cases.

A mains network provides an extensive existing infra-structure. Furtherexploitation of the existing mains infra-structure would beadvantageous. For example, increased functionality, both in terms ofcontrol and monitoring of the power network may be achieved, includingimproved metering and providing additional services to customers.

As a consequence of deregulation in the power supply industry in manycountries, achieving reconciliation of power supplied and determiningthe power used and network losses has become a significant problem. Theproblem arises principally on the low voltage distribution network,where more than one retailer exists as well as a separate to linescompany. There is a need for improved measurement of network losses sothat accuracy in power reconciliation can be improved.

It is thus an object of the present invention to provide a power linecommunication system and method that provides additional functionalityfor one or both of power network management and the provision of networkservices, or at least to provide the public with a useful alternative.

Definitions

Computer controller—computerised apparatus for managing communicationswithin a mains communication network. The computer controller typicallyincludes one or more suitable computer processors, a suitable operatingsystem and suitable application(s). For example and without limitationthe computer controller may be a computer or network of computersoperating Windows NT® or Linux.

Intelligent device—a device that includes a computer processor andassociated memory and a communication interface allowing the device toperform at least some communication functions. Intelligent devicesinclude, without limitation, a relay or meter including a computerprocessor, memory and communication interface.

Power usage profiling—identification of patterns of use of power at aspecific site or by a specific device that is connected to the mainscommunication network.

Utility—a retail supplier of power to customers.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is providedan intelligent device for a power line communication system that hasstored in memory information uniquely specifying the intelligentdevice's identity, includes an interface for data communication with apower line and is operable to perform a configuration process includingthe steps of using said interface to:

-   a) detect data of a first data type through the interface and in    response thereto extract from the data of a first data type and    record in memory identity information for the source of the data of    a first data type and generate on said interface data of a second    data type that have as a destination address the source of the data    of a first data type and includes the information specifying the    intelligent device's identity;-   b) detect data of a second data type that have the intelligent    device as a destination address and in response thereto extract from    the data of a second data type and record in memory the identity of    the source of the data of a second data type and generate on said    interface data of a third data type that includes information    identifying the source of the data of a second data type and the    information specifying the intelligent device's identity;-   c) detect data of a third data type and in response extract there    from and record in memory information identifying the source of the    data of a third data type associated with the information    identifying the source of the data of a second data type included in    the data of a third data type and generate data on said interface    containing the information identifying the source of the data of a    third data type, the information identifying the source of the data    of a second data type included in the data of a third data type and    the information specifying the intelligent device's identity.

Preferably, the data generated in step c) is addressed to at least onesource of data detected in step a).

Preferably, the steps of extracting and recording in step c) are onlyperformed for data of a third data type that are addressed to theintelligent device.

Preferably, the address of the intelligent device is the same as theinformation specifying the intelligent device's identity.

Preferably, the intelligent device is further operable to determine anindicator of the quality of communication between itself and the sourceof detected data and rank identity information recorded in memorydependent on said indicator.

Preferably, the intelligent device is operable to in response todetection of data of a second data type generate data of a fourth datatype including as a destination address the source of the data of asecond data type and the configuration process may further include thesteps of using said interface to detect data of a fourth data type thathave the device as a destination address and in response theretogenerate on said interface data of a first data type.

Preferably, the intelligent device is operable to ignore detected dataof a second data type that were generated by a source that was recordedin memory as a source of data of a first data type in in step a).

Preferably, the intelligent device is operable to use said interface togenerate data of a first data type and wherein the data of a first datatype include a counter, wherein step a) further includes identifying thevalue of the counter of any data of a first data type detected,associate the value of the counter with the recorded identityinformation for the source of the data of a first data type, incrementthe value of the counter and allocate the incremented value to a counterin any data of the first data type generated by the intelligent deviceas a result of data received from the source of the data of a first datatype.

Preferably, the intelligent device is operable to ignore detected dataof a first data type that has a counter value more than a thresholdvalue. Preferably, the threshold value is a value related to the valueof the counter from the last item(s) of data of the first data typereceived. More preferably, the threshold value is one more than thevalue of the counter from the last data of a first data type received.

Preferably, the data of a third data type include a counter and the datagenerated in step c) is in the form of data of a third data type and theintelligent device associates the value of the counter with theinformation recorded in step c) that identifies the source of the dataof a third data type and the intelligent device increments the counterwhen generating data of a third data type in response to detection ofdata of a third data type in step c).

Preferably, the intelligent device is operable to also generate dataonto said interface otherwise than in accordance with the configurationprocess.

Preferably, the intelligent device is operable to generate text messagesonto said interface.

Preferably, the intelligent device is operable to receive controlmessages through said interface and communicate control messages to apower distribution board to facilitate load shed dependent on saidcontrol messages.

According to a second aspect of the present invention, there is provideda power line communication system including a plurality of power linesin communication with a controller through a power line modem, eachpower line having a plurality of intelligent devices as described in thepreceding paragraphs in communication with it, wherein the controller isoperable as one of said plurality of intelligent devices and is also incommunication with a computer controller that is operable to receivedata from the intelligent devices via the controller and to send data tothe intelligent devices via the controller.

Preferably, data other than configuration data, which is generated ontoa power line by an intelligent device or the controller, includes adestination address and an intermediate address, wherein eachintelligent device monitors communications on the power line and if thedestination address of communications matches information identifyingthe source of the data of a second data type included in the data of athird data type that was recorded by an intelligent device in accordancewith step c), then that intelligent device regenerates the data, butwith the intermediate address field comprising the informationidentifying the source of the data of a third data type recorded in stepc) that is associated with the information identifying the source of thedata of a second data type included in the data of a third data typethat matches the destination address.

According to a third aspect of the present invention, there is provideda power line communication system including a plurality of intelligentdevices in communication with a power line operable to monitor energyusage at a site and communicate usage data onto the power line and acontroller also in communication with the power line, wherein eachintelligent device maintains a routing table identifying a first set ofother intelligent devices downstream of it relative to the controllerthat it can communicate with directly and identifying a second set ofother intelligent devices downstream of it relative to the controllerthat it can communicate with through one or more of the first set ofother intelligent devices.

Preferably, the routing table further identifies a third set of otherintelligent devices upstream of it relative to the controller that itcan communicate with directly.

Preferably, the routing tables are formed by an interrogation processinitiated by the controller that requests the intelligent devices thatcan receive data directly from the controller over the power line torespond with information identifying what other intelligent lo devicesthe intelligent devices that can receive data directly from thecontroller over the power line can communicate with either directly orthrough further intelligent devices, wherein the intelligent devicesthat can be communicated with through said further intelligent devicesare identified through an interrogation process conducted by saidfurther intelligent devices.

Further aspects of the present invention may become apparent from thefollowing description, given by way of example of preferred embodimentsonly and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: shows a diagrammatic representation of a power linecommunication system in accordance with an aspect of the presentinvention.

FIG. 2: shows a block diagram of a meter in accordance with the presentinvention.

FIG. 3: shows a block diagram of a controller in accordance with thepresent invention.

FIG. 4: shows a representation of the information and functionsperformed by the database in the communication system of FIG. 1.

FIGS. 5 a, b: show diagrammatically an example of configuration packetcommunications in the communication system of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a mains communication andcontrol network 100 in accordance with the present invention. The mainscommunication and control network 100 includes a mains communicationnetwork 1. This forms the lower levels of a hierarchal communicationsnetwork topology that supplies power to customer sites 8 a-i that areconnected to the mains communication network 1 and also forms a lowvoltage sub-network of a larger mains network 101, which typicallyincludes a high voltage network that supplies high voltage three phasepower to the mains communication network 1.

A computer controller 2 provides the upper levels of the communicationsnetwork topology. The computer controller 2 includes, in this example ofa preferred embodiment, a central control unit 2A, which communicateswith the mains communications network 1 through a communicationscontroller 2B. A database 2C is provided for the central control unit2A, containing the necessary control information for the mainscommunication network 1 and also containing power use information fromthe mains communication network 1. Customer billing may be managed by abilling system 2D.

The mains communication network 1 shown in FIG. 1 may be one low voltagesub-network of many in the wider mains network 101. The communicationscontroller 2B may communicate with a large number of such sub-networks.

The mains communication network 1 includes a controller 3, which issuitably located at a transformer 4. The transformer 4 may receive highvoltage power from the mains network 101 and output low voltage power tothe rest of the mains communication network 1. The computer controller2, particularly the communications controller 2B may communicate withthe controller 3, through for example a wireless communication channel5. Other communication channels may be used.

The controller 3 includes three power line modems 6, one modem per phase7 a-c of the mains communication network 1 on the low voltage or demandside of the transformer 4. The power line modems 6 may, for example usea power-line carrier employing FSK modulation with a carrier frequencyin the range of 67 kHz to 87 kHz. Each phase 7 a-c feeds into a numberof the customer sites 8 a-i. Each of the customer sites 8 a-i includes ameter 9, with each meter 9 being an intelligent meter. Some furthercustomer sites connected to the phases 7 a-c may not have intelligentmeters, but these are unimportant to the operation of the presentinvention and therefore are not shown in the accompanying drawings ordescribed herein.

The mains communication network 1 may include one or moremicro-generation or energy storage facilities 14. In FIG. 1, twomicro-generation/energy storage facilities 14 are shown. Themicro-generation/energy storage facilities 14 may represent for example,small hydro-generators, solar-generators, wind-generators or fuel cellsand may be located at any one or more of the customer sites 8 a-i or beseparate from the customer sites 8 a-i. The micro-generation/energystorage facilities 14 each include a meter 9A.

The communication functions of the mains communication and controlnetwork 100 are now described with reference to the example function ofmeter data collection. The controller 3, through the appropriate powerline modem 6, polls a meter 9 for the power consumed at a site 8 a-isince the last time the associated meter 9 at the site was polled. Themeter 9, which includes its own transmitter, then sends informationindicating the power consumed to the controller 3, where it is buffereduntil requested by the computer controller 2. The central control unit2A then initiates a communication session with the controller 3 throughthe communications controller 2B, which receives the bufferedinformation through the communication channel 5. The central controlunit 2A then updates the database 2C with the newly receivedinformation. The billing system 2D may then generate a bill at arequired time, based on the information stored in the database 2C. Inaddition, the updated billing information may be sent by the centralcontrol unit 2A to the meter 9 for display on the customer display unit10.

Each meter 9 used in the mains communication network 1 is an intelligentpower meter. Typically, the meter 9 will replace any existingelectro-mechanical meter at each customer site 8 a-i. A block diagramrepresentation of a meter 9 is shown in FIG. 2. The meter 9 includes acomputer processor 900, which may for example be a Dallas 5002FP, 8051compatible processor. External memory 901, which may be SRAM, isprovided in communication with the processor 900 and the operations ofthe processor 900 are timed by a clock 902. The meter 9 also includesEEPROM 903. The meter 9 may communicate with optional external devices,through a serial communications interface 904. The meter 9 may alsoinclude its own display 905 for communication of information to users. Apower line modem 906 allows the meter 9 to communicate with thecontroller 3 through a phase of the mains communication network 1.

The meter 9 records the power usage using an energy measurement module907. For example, the energy measurement module may be a SAMES SA9102Cenergy-metering integrated circuit, available from South AfricanMicro-Electronic Systems, Pretoria, South Africa. The resulting data isstored in memory 901 using an encryption algorithm. Bidirectional energymeasurement modules are also available from South AfricanMicro-Electronic Systems for use in a bidirectional meter.

The EEPROM 903 contains the starting meter count, the number of pulsesfor each kilowatt hour, the number and type of connections to the meter,type of devices attached to the serial communications interface 904, andthe functions of any additional outputs. Identification information forthe meter 9 that identifies the meter from other meters, referred toherein as an electronic serial number, is also stored in a protectedpart of the EEPROM 903.

The computer processor 900 has precedence over communications while themeter reading is accumulated in hardware. A hardware register (notshown) provided for the meter reading is read by the computer processor900, then reset when the communications channel is not in use.

When the central control unit 2A sends a poll to a meter the pollincludes a specification of the current time. Upon receipt of a timepacket from the central control unit 2A, the communications controller2B sets its clock if it differs from that in the time packet. The timepacket will be queued together with all the other packets for sending tothe controller 3 when the connection is established. During the time thepacket is queued for transmission, the current system time will continueadvancing. Therefore, when the connection is established, and the timeis forwarded to the controller 3, the time fields of the packet will beupdated to the current system time.

Data is requested from each meter 9 by the controller 3 periodically,for example once every several hours. Contained in the request for datapacket (initiated by the controller) is the correct time. The meter 9will therefore be refreshed with the correct time periodically. Thevariable transmission delay to the meters 9 should also be accountedfor. Since each message is acknowledged, the round trip time divided bytwo can be calculated, and may be referred to as the latency. Thecontroller 3 sends each individual meter 9 a time signal corrected bythe latency applicable to that meter 9. The latency used for a currenttransmission may be based on historical information or a furthercommunication from the controller 3 may cause the meter 9 to advance itstime.

One of the optional external devices that may be connected to the meter9 through the serial interface 904 is a customer display unit 10. Thecustomer display unit 10 may have increased display capabilities anddisplay information to the customer, such as the amount due since lastpayment, recent consumption information and the total meter reading. Inaddition, messages sent from the central control unit 2A or fromelsewhere to the meter 9 may be displayed on the customer display unit10.

FIG. 3 shows a block diagram of a controller 3. The controller 3includes a processor 300 for controlling the three power line modems 6a-c through serial communication buses and manages the receipt,transmission and storage of information from the various meters 9 andfrom the communications controller 2B. A memory 301 is provided to storea routing table (see herein below) and a communications interface 302,suitably a wireless communications interface, is provided to allowcommunication with the communications controller 2B.

The communications controller 2B is a real time processing system thatlinks the central control unit 2A and database 2C with each controller 3and subsequently each meter 9. The communications controller 2B maycommunicate with the central control unit 2A via a serial communicationslink or Ethernet using TCP/IP. Where the meters 9 in the mainscommunication network 1 can generate alarms, the communicationscontroller 2B preferably receives the alarm signals and forwards theseon to the central controller 2A. The communications controller 2Bincludes an interface to communicate with the controller 3, which inFIG. 1 is a wireless interface, although a leased line modem, standarddial up modem, or fibre-optic modem may be used instead. As statedherein above, the communications controller 2B preferably communicateswith a plurality of controllers 3.

The central control unit 2A stores an operating system such as WindowsNT®. It also includes appropriate software to manage the database 2C.The central control unit 2A performs essentially two main functions, thefirst being to manage the database 2C and the second to control thefunctions of the mains communication network 1.

FIG. 4 shows a representation of the functions of the database 2C. Powerusage data from each meter 9, which has been received through thecontroller 3 and communications controller 2B, is stored in memory. Thedatabase 2C may include an analysis function to analyse the raw powerusage data and provide specific output results. A query functionalitymay be provided to allow the billing system 2D to retrieve either orboth of the raw power usage data or results of the analysis function. Inaddition, the database 2C may store the routing tables that dictate thepath that data communications take through the mains communicationnetwork 1. The formation and use of the routing tables are described inmore detail herein below. The central control unit uses the routingtables when sending out information to the meters 9. Database 2C mayalso include the location and technical specification of each controller3 and each meter 9. The controllers 3 and meters 9 may be identified inthe database 2C by their electronic serial number, which is used by thecentral control unit 2A to distinguish between the various controllers 3and meters 9 and also to allow each controller 3 and each meter 9 toidentify the information communicated within the mains communicationnetwork 1 that is destined for it. The location information may be usedfor the purposes of billing, repair of faults and for intelligentrelaying.

The computer controller 2 may perform statistical analysis of the usagedata, which may be periodically updated, to provide power usageprofiling. The power usage profiling may assist a power utility in theestimation of demand, for instance, by profiling supply from particulardistribution transformers 4 to their respective mains communicationnetwork 1. The power usage profile for the customers of a utilitysupplied from a particular grid exit point provides a current inventoryof energy usage. The utility may therefore determine in an almostreal-time manner what its bill for supply from that grid point shouldbe.

Power usage profiling may also benefit a utility in terms of assetmanagement. Specifically, the power usage profile obtained from thecontroller 3 provides information on the load profile for its associatedtransformer 4 and phases 7 a-c. Changes in usage pattern can be used todetect certain events, such as loss of supply to an area caused by adistribution fault, accidental disconnection of individual premisesand/or to indicate tampering/fraud. It also provides the utility withaccurate, monitored, quality of supply (i.e. outages) information. Suchinformation is of use for scheduling asset maintenance, upgrades andreplacement. Preventative maintenance may be assisted by monitoring thequality of network assets. This may be achieved by measuring changes inpower line communication quality through the network. Information aboutcommunication quality is retrieved periodically. Specifically, bit errorrate tests may be performed routinely during auto-configuration of thenetwork and packet error rate tests can also be performed on request. Byidentifying trends of increasing error rates over time, ageing networkassets can be identified.

The above described functionality, together with many other functionsthat may be provided, for example by other external devices connected tothe meter 9, require bi-directional communication between the mainscommunication network 1 and computer controller 2 and within the mainscommunication network 1. An important aspect of the present invention isthe method of communication between these two networks and within themains communication network 1. To establish the communication channels,a number of routing tables are formed and stored in the computercontroller 2 and mains communication network 1. The routing tablesidentify the various paths that communications may take between thecomputer controller 2 and mains communication network 1, in particularbetween the central control unit 2A and each meter 9.

Formation of Routing Tables

The central control unit 2A and the controllers 3 are the primarycontrollers in respect of the formation of routing tables. The centralcontroller 2A uses a priori knowledge of the network topology toseparate the various meters 9 into several sets, each set defined by allthe meters 9 and their attached optional devices connected to a singlephase of a particular transformer 4. The controller 3 is responsible forforming the routing table for the phases in which it is in communicationwith. This subdivision may reduce the time to create the routing tablesand facilitate the recreation of sections of the logical network definedby the routing tables to overcome local communication problems.Recreation of the logical network may be achieved by a controllersending out WCHM packets (see herein below) and waiting for responses inthe same way that the logical network is first created.

Referring now to FIG. 5, a diagrammatic representation of the packetflows for establishing the routing tables is shown. Upon initialisation,or upon prompting by the central control unit 2A, the controller 3generates and transmits to each of its serial communication buses apacket of a first type, referred to herein as the WHO_CAN_HEAR_ME (WCHM)packet. The power line modems 6, which are intelligent modems, eachreceive the WCHM packet and in response thereto send back to thecontroller 3 a packet of a second type referred to herein as anI_HEAR_YOU (IHY) packet. The IHY packet indicates to the controller 3that a modem is present on that serial communication bus and includes afield containing the electronic serial number of the modem. Thecontroller 3 records how many power line modems 6 it is in communicationwith, their electronic serial number, and on which serial bus they arelocated. The controller 3 may then collate the IHY packets and send apacket to the central control unit 2A of a third type referred to hereinas an I_HEARD_THESE (IHT) packet that specifies the electronic serialnumber of each modem.

The controller a may then send a packet of a fourth type, referred toherein as the WHO_CAN_YOU_HEAR (WCYH) packet. The WCYH packet promptseach power line modern 6 to generate a WCHM packet on its output, whichrepresents one of the phases 7 a-c of the mains communication network 1.The WCHM packet includes the electronic serial number of the power linemodem 6 that sent the packet. The power line modem 6 may optionally havethe same electronic serial number as the controller 3 to which it isconnected. Optionally, the power line modems 6 (and meters 9) mayautomatically generate, after a predetermined delay, a WCHM packet afterreceipt of a WCYH packet.

Each meter 9 at each customer site 8 a-8 i monitors the phase to whichthey are connected and upon receipt of a WCHM packet by a meter 9, themeter 9 enters the electronic serial number in the WCHM packet into itsrouting table as a primary parent i.e. a device from which it canreceive communications directly. The meter 9 responds to the WCHM packetwith an IHY packet addressed to the source of the WCHM, which in thiscase is a power line modem 6. The IHY packet includes a field containingthe electronic serial number of the meter 9 that received the WCHMpacket. The power line modems 6 receive the IHY packets from the variousmeters 9, collate these and send notification to the controller 3identifying each meter 9 that responded to their respective WCHM packetin an I_HEARD_THESE (IHT) packet, which includes the electronic serialnumbers contained in all the IHY packets received. The controller 3 thenenters in its routing table the electronic serial numbers from the IHTpacket as a primary child i.e. devices to which it can send informationdirectly using it associated power line modems 6.

Referring now to FIG. 5 b, the controller 3 then sends out a WCYH packetto each primary child meter through the appropriate power line modem 6.Each primary child meter 9 acknowledges receipt of the WCYH packet andalso generates a WCHM packet on its output, which is a phase from thetransformer 4. In an alternative embodiment, each meter 9 mayautomatically generate a WCHM packet after receiving such a packet. Eachmeter 9 that receives this WCHM packet returns an IHY packet. Eachprimary child meter 9 records in its routing table as primary childrenthe electronic serial number of all meters that returned an IHY packetto it and each meter 9 that received a WCHM packet adds the primarychild meter as a direct parent in their individual routing table. Eachprimary child meter 9 also sends through its power line modem 906 an IHTpacket to the controller 3 through the power line modem 6 indicating theelectronic serial number contained in IHY packets that it received. Thecontroller 3 then adds the electronic serial number as secondarychildren in its routing table (i.e. meters that can be communicated withvia another meter logger). The controller 3 also associates eachsecondary child with each of the primary children that sent an IHTpacket containing the electronic serial number of that secondary child.This enables the controller 3 to identify to which primary childinformation should be sent in order to reach a particular secondarychild.

Each meter 9 identifies two or more paths back to the controller 3. Toachieve this, each meter 9 records the electronic serial number of anymeter from which it received a WCHM packet. The source of the first WCHMpacket received could be identified as Parent 1. The source of thesecond WCHM packet received could be identified as Parent 2. Similarly,the sources of any subsequent WCHM packets could be recorded asGuardians. The Parent and Guardian meters thus identified representalternative paths back to the controller 3.

The above configuration process continues, with the controller 3 sendingWCYH packets to each secondary child through the appropriate primarychild in order for it to identify its tertiary children. The controller3 then sends WCYH packets to the tertiary children through the primaryand secondary child meter loggers and so on until all meters 9 have beenentered into the routing table of the controller 3. Each meter 9maintains its own routing table, extracting the electronic serialnumbers from IHT packets received from its direct children andassociating the serial numbers with its direct children. Thus, eachmeter knows all the other meters with which it can communicate directly(its parents and primary children) and also knows all the meters it cancommunicate with indirectly through each of its primary children.

The IHT packets may be addressed to the parents of a meter or simplytransmitted onto the power line. If the IHT packets are addressed,recipient parent meters may simply record the identity information ofthe secondary children associated with the identity information of thesender of the IHT. The recipient meters then forward the IHT packets totheir parents, who will forward the packet to their parents, associatingthe identity information contained in the packet with their relevantprimary child and so on until the controller 3 receives the packet. Ifthe IHT packets are not addressed, then each recipient meter comparesthe source of the IHT packet to all of its children and adds theidentity information in the IHT packet only if there is a match. Therecipient meter associates the identity information in the IHT packetwith the child that matched the source of the IHT packet and thenaddresses the IHT packet to its parents.

To avoid continuous loops in the configuration process, each meter 9ignores IHY packets that it receives containing the electronic serialnumber of any meter that is listed as a parent. Also, should theidentity information in any IHT packet match a parent of the recipientmeter or itself, the IHT packet is ignored.

In one embodiment, when the controller 3 transmits a WCHM packet, itimmediately follows this with a bit error rate test. Each meter 9 willreceive the WCHM packet and bit error rate test and respond with an IHYpacket and a quality indicator based on the bit error rate test. Eachmeter 9 also sends a bit error rate test when it sends a WCHM. Thus, thecontroller 3 and each meter 9 can record for each meter that it is incommunication with, the quality of the communication path to that meter.This process allows each meter to rank the various communication pathsto both its parents and its children, using the highest qualitycommunication path first. If the communication path of highest qualityshould fail, for example by failure to receive an acknowledgement ofreceipt packet, the controller 3 or meter 9 uses the next highestquality communication path, if one exists.

The network configuration packets WCHM, IHY, WCYH and IHT are used tocreate a logical power-line network structure. At least selected ofthese configuration packets contain the electronic serial number of thecontroller 3 and this electronic serial number is relayed by each meter9. For example, each WCHM packet contains the electronic serial numberof the controller 3. Where a meter sends the WCHM packet, it determinesthe electronic serial number from the WCYH packet that it received.Every meter 9 stores the electronic serial number of its controller 3 inEEPROM 903. This logical network, the structure of which is determinedby the parent and child links in the routing tables, will be updatedperiodically to ensure that the logical network remains current.

The system may also recreate the logical network on the occurrence ofone or more particular events. Any device within the mains communicationnetwork 1 may transmit onto its associated phase a packet referred toherein as a NETWORK_CHANGED (NC) packet. Typically, it will be themeters 9 at any of the customer sites 8 a-i that will transmit a NCpacket. During the lifetime of a logical network between periodicupdates, the network may change, for example due to routine maintenance(e.g. a street may be switched to another phase of a transformer) or byadding or removing meters 9. If this happens the new meter, or one thatwas previously connected to a different controller, will detect thetraffic on the network and notice a different controller electronicserial number in the packets communicated over the phase to which it isconnected. When this happens, that meter will send a NC packet onto thephase and meters 9 that detect the NC packet, relay the packet to thecontroller 3, which initiates a recreation of that part of the network.

The variable noise and attenuation on the mains network has significantconsequences for meter communications. Specifically, meters that couldbe contacted at the time the logical network was last configured (eitherat a pre-programmed time or as a result of a NETWORK_CHANGED packet) maynot necessarily be contactable at some later instant. Maintainingcommunications between the central control unit 2A and each meter 9 maybe particularly important for real time control of the mainscommunication network 1, for example to provide for load shed.

The central control unit 2A maintains a list of all contactable meters9. To achieve this, the controller 3 sends out PING packets toindividual meters 9 in its routing table, at times when there is noother network traffic, and monitors the responses to build a list of thecurrently contactable meters 9. Meters 9 that were in the logicalnetwork when it was created but can't now be contacted are thereforeidentified. Should they remain out of contact using the current routingtable for a certain predetermined period, a local network recreation isinitiated by the controller 3. In addition, if a meter 9 is unable tocontact another meter 9 (determined by failure to receive anacknowledgement or other return information) after a predeterminednumber of tries, for example three attempts using all available paths,an error is generated by the transmitting meter and sent to thecontroller 3. Should the meter remain out of contact for too long aperiod, a local network recreation is initiated by the controller.

A manual over-ride may be provided to allow for the recreation of thelogical network on demand and to specify fixed communication channelswithin the logical network. For example, the central control unit 2A maysend packets referred to herein as YOU_HEARD_THESE (YHT) andYOUR_PARENT_IS (YPI). These packets respectively identify the meter'schildren and its parent or parents and guardians.

The quality of communications between meters can be determined by use ofa packet error rate test. The central control unit 2A can request acontroller to initiate a packet error rate test between any desiredmeters. A known signal is transmitted, including a signature identifyingit as a packet error rate test. The recipient meter 9 records the errorrate and forwards this to the controller 3. The controller 3 in turnforwards the result to the central control unit 2A. Should the packeterror rate test results be unacceptably low, the options available tothe central control unit 2A include initiating a local networkrecreation or manually reconfiguring the meters routing tables using theYHT and the YPI packets. Communication quality indicators other than apacket error rate test may be used if required.

When the logical network is recreated, the previous logical network issaved as a backup network. This allows reconstruction of a previousworking logical network should the new network be inoperable for somereason.

In the foregoing example of formation of routing tables, only a twolevel table in the child direction is formed in each meter—its directchildren and all the meters that the direct children can communicatewith. The meter does not know whether any child is a secondary, tertiaryor higher level child. Similarly, the controller 3 and central controlunit 2A do not know where each meter is in the hierarchy apart from theprimary children of the controller 3. Also, only the direct parents arerecorded. This embodiment is preferable as reducing the memoryrequirements for the routing tables and reducing network communicationsfor establishing the logical network.

In an alternative embodiment, a counter may be added to the IHT packets,which is incremented each time the IHT packet is relayed to a parent.Therefore, each meter knows how far away each meter is in terms oftransfers through other meters. The IHT meters may also include aquality indicator that provides an accumulated indication of the qualityof communication between meters, taking into account the retransmissionsthat take effect. This information can be associated with each child andused by the meters and the controller that receives the IHT packet tochoose a path to a particular meter. Each meter may then, either knowhow many steps away each meter is or alternatively know the meters thatare one, two, three, four and five steps away, with those that are morethan five steps away being grouped together.

Also, a counter may also be associated with each WCHM packet, which isincremented each time a meter sends out a new WCHM packet. A meter mayignore a WCHM packet if the counter in it is too much higher than thecounter in the last WCHM packet they received. For example, to achievean efficient routing table, if the counter in a WCHM packet is two ormore values higher than the counter in the last WCHM packet, it may beignored.

The WCYH packets may further accumulate in order the electronic serialnumbers of all the meters through which it ‘travelled’ so that eachmeter can record fully the path back to the controller 3, or at leastmore than one step back to the controller 3.

Data Communication

During operation, each meter 9 listens to all communications on thephase 7 a-c to which it is connected. Each packet transmitted onto thenetwork by a device contains the electronic serial number of the sourceof the packet, the electronic serial number of the device that is thefinal destination for the packet, and an intermediate meter electronicserial number if a relay is required. The packet is received by a meter9 designated as the intermediate one (if one is designated), and thatmeter will change the intermediate meter electronic serial number to thenext meter in the path to the device having the destination electronicserial number (using information stored in its routing table) andtransmits the modified packet.

The meter identifies the appropriate route over which to transfer apacket by a software routine that examines its routing table uponreceipt of a message destined for another meter or for the controller.The destination of any message is dictated by an electronic serialnumber field. If the message destination is the controller 3, then themeter 9 forwards the message to its parent. The parent repeats theprocess and forwards the message to its parent and so on until themessage is delivered to the controller. If the message destination isanother meter, the meter that received the message examines its routingtable to see if the destination meter is a child. If so, the routingtable is further examined using a software routine that identifies theappropriate intermediate destination of the packet. This routine worksbackwards from the destination electronic serial number to identify itsparent, and then the parent of that parent and so on until it is onelevel below the meter that has received the message. This may only everbe a two stage process if the meter does not know how far away othermeters in its routing table are. The packet is then despatched to thisintermediate destination meter and the process repeated.

Each packet is sent by a particular device in the network to anintermediate meter up to three times before flagging an error and givingup on that communications path. If the communications fail on anupstream path (i.e. the message is being relayed to the controller) thenthe meter will try to relay the message through its second parent.Should this route also fail, then the message will be relayed throughone of the guardian meters. If this also fails and the communicationsdon't get through to a meter one level upstream (i.e. closer to thecontroller) the meter is designed to attempt to jump over the meter justupstream and attempt to communicate with one further upstream. This isdone by examining the routing table and identifying the parent's parent(if this information is available) and relaying the message through thismeter. Should communications fail on the downstream path (i.e. themessage is being relayed from the controller) the meter is designed toattempt to jump over the meter just downstream and attempt tocommunicate with one (two levels) further downstream. This is done byexamining the routing table and identifying the intermediate electronicserial number that would have been used by the meter that wasn'tresponding, and relaying the signal directly to this intermediateelectronic serial number.

If all else fails (on either upstream or downstream paths), a meter 9may request help, using a packet referred to herein as a HELP_TRANSPORTpacket, from any meter that can provide an alternate path to thedestination meter or controller. Responses to this HELP_TRANSPORT packetare examined and a choice is made as to which of these to use as thenext intermediate meter. The packet will be forwarded to this meter, byupdating the intermediate meter electronic serial number to match thatin the selected response and that meter will take over theresponsibility of getting the packet to the next intermediate or finaldestination meter. The sending meter may optionally update its routingtable to include as a child the new intermediate meter in the path tothe destination meter to which it was originally trying to send.

The data section of the packets should be encrypted, but the datasection control word should not be encrypted. The data section controlword must be immediately recognisable to allow alarm traffic to takeprecedence over other types of information, and to allow the time datato be updated as it is being transferred from meter to meter.

Some mains communication networks may not have a controller 3, perhapsdue to being of such a small size that a controller can not bejustified. In FIG. 1, a diagrammatic representation of such a network isreferenced 1A. The mains communication network 1 may be used to relaydata to the mains communication network 1A. One or more specific meters9, for example the meter 9 at customer site 8 i acts as a relay to themains communication network 1A, in particular to one or more meters 9Bthat can communicate with the meter at site 8 i. The link betweennetworks may be provided via a radio or dial-up telephone connection, inwhich case the meters designated as the link between networks areprovided with the appropriate radio or telephone modem 11. The routingtables of the link meters and of the meters in the subsidiary networkare manually configured using the network configuration packetsdescribed herein above YOU_HEARD_THESE (YHT) and YOUR_PARENT_IS (YPI).

To increase communication reliability, the packets are broken up intosmall pieces and reassembled by the destination meter or by thecontroller modem. The size of the packets is an important designvariable for any mains communication network and size selectiontypically represents a trade-off between reliability and efficiency ofcommunication.

To determine the maximum permissible packet size, an experimental methodmay be used. Over a period of time sufficiently long to represent anormal range of conditions over the network, which may be as long asseveral months and at various times of the day and under a variety ofweather conditions, the mains communication network is sounded usingmeters equipped with bit error rate software. One meter continuouslytransmits while the other meters operate in receive mode. A knownpattern is sent and time-stamped errors are stored by the receivers.These error files are then analysed to determine that the noise on thechannel is bursty in nature and this may be used to determine theoptimum packet size.

Differing length packets are used to convey information, with very shortpackets reserved for high priority messaging and longer packets up tothe maximum length used for low priority messaging. For example alarmmessages and load shed control signals (see herein below) may take thehighest and second highest priority and have the lowest packet length.

Upgrading of Software

A potential disadvantage of intelligent meters is the difficulty ofupgrading software to enhance functionality. Typically in prior artsystems this can only be achieved by physically visiting each site,temporarily taking the meter out of service and downloading new softwareinto the meter. The meters 9 of the present invention are provided witha computer processor 900 capable of In-Application-Programming (IAP) toenable remote software updates. The STMicroelectronics uPSD3234Amicrocontroller, available from STMicroelectronics of Geneva,Switzerland, supports IAP and includes dual banks of flash memory and acontrol register to allow its 8032 controller to run from one flash bankwhile erasing and updating the other bank. More than one version of themeter software can be stored in each meter 9, so that it is possible todrop back to an earlier version of the software if problems arise. Thecapability of remote software updates also permits the change of modemcarrier frequencies and baud rate to enhance message transfer.

Network Loss Measurement

As a consequence of deregulation in the power supply industry,reconciliation of power supplied, power used and network losses hasbecome a significant problem. The problem arises principally on the lowvoltage sub-network, where more than one retailer exists as well as aseparate lines company. An additional meter, a low voltage master meter12 may be provided to solve this problem. Specifically, the low voltagemaster meter 12 is a device placed between the distribution transformer4 and the controller 3 that measures the total power supplied from thetransformer 4 over all three phases. This power supply figure may bemetered, for example, on a half-hourly basis and accumulated resultsforwarded to the controller 3 on a periodic basis. When all use datafrom the meters 9 and the power supply figure from the low voltagemaster meter 12 has been returned to the central control unit 2A, thedatabase 2C can be used to determine line loss as the difference betweenpower supplied and power used.

In addition, the efficiency of the transformer 4 may be measured. Thelow voltage master meter 12 and a high voltage meter 13 with pulseoutput remotely monitor distribution transformer efficiency.Specifically, the high voltage meter 13 is placed on the primary of thedistribution transformer 4. It reads input 3-phase power on ahalf-hourly basis. The low voltage master meter 12 records total poweroutput from the transformer on a half-hourly basis. At fixed intervalsthe controller 3 requests the half-hourly readings from both the highvoltage meter 13 and the low voltage master meter 12 and stores thesereadings for subsequent forwarding to the central control unit 2A anddatabase 2C. The database 2C is then able to use these readings todetermine transformer efficiency.

Private-Side Applications of Mains Communication Network

The mains communication network described herein provides increasedflexibility in the control of the power network and in the provision ofadditional services to customers. Examples of new applications forcustomers are provided below.

The mains communication network 1 may monitor the status of variousdevices and machines. This is achieved by connecting a serial interface904 of a meter 9 to the device or machine. For domestic premises, anintelligent PLC relay can be used to automate a device or monitor anessential device such as a dialysis machine in the home. For hospital orrest-home applications, an intelligent PLC relay can be used to remotelymonitor (for example from a nurse's station) the status of an essentialpiece of mains-powered equipment at a patient's bedside.

For residential “community” developments, the meters 9 may be used toautomate the front gate and other limited or restricted access pointssuch as a pool complex and for control of external lighting without theneed for individual wiring to each dwelling. In one embodiment, abody-corporate residential development may have “always-on” web accessin which all key control points (e.g. front gate and pool gates) have aweb-cam in communication with a phase 7 a-c, which links back to theresidential development's central office, which is also on a phase 7a-c. Residents could then access the central office through the web toview the web-cam picture and grant or decline access. The caretaker ormanager of the complex would have the ability to over-ride access ortime-of-day controlled features by accessing the central office via theweb. An advantage of this system is that individual wiring to eachpremises is not required.

The meters 9A in FIG. 1 may be dual meters. The meters 9A facilitate themonitoring and control of energy storage devices and of embeddedgenerators so that their energy is made available to the grid atappropriate times. This control, when used in combination with powerusage profiling, allows improved management of the energy supply withinthe entire mains communication network 100. A benefit of this may be areduction in the need for spinning reserve. Specifically, the currentpower usage profile can be used (in combination with “historical”records) to determine when embedded generators should be turned on. Suchgenerators could be switched on either by their owners or remotely bythe utility by instructing the central control unit 2A to send anappropriate packet.

Furthermore, improved network management may be achieved using loadshedding. The meters 9, together with an appropriate distribution board15 (see FIG. 1) connected to the serial interface 904, permit remoteload shedding. Specifically, a customer may offer up appliances forremote load shedding. The utility monitors customer power usage over ashort period, say 2 months. On the basis of the power usage profile sodetermined, the utility offers the customer 6 special billing rate inreturn for permitting the utility to remotely shed load at thecustomer's premises. In addition, the customer can view their usageprofile, via the web, and use this information to alter their usagepattern if appropriate. Load shedding is achieved by the central controlunit 2A sending a LOAD SHED PACKET to a meter 9, the LOAD SHED PACKETdesignating the device that should be disconnected by a distributionboard 15. The meter 9 then instructs the distribution board 15 to makethe appropriate switching.

In one embodiment of the invention, power usage profiling may be used toindicate illness, for example by a significant increase or decrease inpower usage or lack of change in power usage over an extended period.Specific customer sites 8 a-8 i may request a follow up call or visitshould their power usage change (or not change) significantly to checkthat they are not immobilised or seriously unwell. Specifically,consumers with serious medical problems, who wish to remain livingalone, can identify themselves to the utility and request monitoring oftheir power usage profile on a near real-time basis. Should their powerusage profile depart significantly from the norm, notification of apotential problem is raised by the central control unit 2A to anadministrator.

Using the infrastructure of the present invention, customers may beprovided the option to have a dual-tariff agreement. At present, twometers are required to log power usage for customers on a dual tariffagreement. One meter is used for one particular tariff period andswitched off at the time when the second tariff applies. Usage duringthe second tariff period is recorded on the second meter. Within thetariff periods no information is normally available on time-of-use, withthe meter simply recording total usage. By using a meter 9 with theinfrastructure of the present invention, including the database 2C,there is no need for a second meter. Reconciliation with the dual tariffstructure can be achieved using records stored in the database 2C.

In some cases, customers may prepay their power account. Previously, ifthe account became in deficit or became in deficit for a certain periodand/or by a certain amount, the supply of power would be discontinued.When the database 2C detects an account in deficit beyond some defined“grace period”, the load shedding functionality is used to disconnectthe bulk of the supply to the premises. The system could provide suchcustomers only with an emergency supply, for example supply sufficientfor lighting and a small amount of heating.

Text messages may be distributed via power line carrier. Specifically,via their meter 9 or customer display unit 10, a customer can arrange toreceive text messages from and send text messages to, for example themeters 9 of other individuals, a structure (e.g. a body corporate), orto a wide area network 16 via the central control unit 2A. Advertisingfor a local community may be provided using the text messagefunctionality. Specifically, individual consumers with a meter 9 canauthorise their utility to add their electronic serial number to anaddress list for local advertisers or community groups. Local businessesand community groups can then arrange to have advertising messages orcommunity notices forwarded to these consumers via the central controlunit 2A.

For applications where an alarm is generated, in addition to the usualalarm notification procedures, a text message may be sent to theneighbouring properties should an alarm be triggered. Should an intruderbe on the premises, it is likely a neighbour could notify the Police inadvance of the arrival of a security guard. Also, nominated contacts(such as nearest neighbours) may be sent a text message when a medicalalarm is tripped or when the “at risk” power usage profile threshold iscrossed. Such notification would be additional to any telephone contactspecified in the event of an alarm. The telephone contact may beinitiated directly by the meter 9 through a telephone modem connected toits serial interface 904 or alternatively by the central control unit 2Ain respect to the alarm notification.

Where in the foregoing description reference has been made to specificcomponents or integers having known equivalents, then those equivalentsare hereby incorporated herein as if individually set forth.

Although the foregoing description of the invention has been given byway of example with reference to the accompanying drawings, thoseskilled in the relevant arts will appreciated that modifications orimprovements may be made thereto without departing from the scope of theinvention as defined in the appended claims.

The claims defining the invention are as follows:
 1. An intelligentdevice (9) for a power line communication system (100) that has storedin memory (903) information uniquely specifying the identity of theintelligent device (9) and includes an interface (906) for datacommunication with a power line and is operable to perform aconfiguration process including the steps of using said interface (906)to: a) detect data of a first data type (WCHM packets) through theinterface and in response thereto extract from the data of a first datatype (WCHM packets) and record in memory identity information for thesource of the data of a first data type (WCHM packets) and generate onsaid interface (906) data of a second data type (IHY packets) that haveas a destination address the source of the data of a first data type(WCHM packets) and includes the information specifying the identity ofthe intelligent device (9); b) detect data of a second data type (IHYpackets) that have the intelligent device (9) as a destination addressand in response thereto extract from the data of a second data type (IHYpackets) and record in memory the identity of the source of the data ofa second data type (IHY packets) and generate on said interface (906)data of a third data type (IHT packets) that includes informationidentifying the source of the data of a second data type (IHY packets)and the information specifying the identity of the intelligent device(9); c) detect data of a third data type (IHT packets) and in responseextract there from and record in memory information identifying thesource of the data of a third data type (IHT packets) associated withthe information identifying the source of the data of a second data type(IHY packets) included in the data of a third data type (IHT packets)and generate data on said interface (906) containing the informationidentifying the source of the data of a third data type (IHT packets),the information identifying the source of the data of a second data type(IHY packets) included in the data of a third data type (IHT packets)and the information specifying the intelligent device's identity.
 2. Theintelligent device of claim 1, wherein the data generated in step c) isaddressed to at least one source of data detected in step a).
 3. Theintelligent device of claim 2, wherein the steps of extracting andrecording in step c) are only performed for data of a third data typethat are addressed to the intelligent device.
 4. The intelligent deviceof any one of claims 1 to 3, wherein the address of the intelligentdevice is the same as the information specifying the intelligentdevice's identity.
 5. The intelligent device of any one of claims 1 to 4further operable to determine an indicator of the quality ofcommunication between itself and the source of detected data and rankidentity information recorded in memory dependent on said indicator. 6.The intelligent device of any one of claims 1 to 5, operable to inresponse to detection of data of a second data type generate data of afourth data type including as a destination address the source of thedata of a second data type and the configuration process may furtherinclude the steps of using said interface to detect data of a fourthdata type that have the device as a destination address and in responsethereto generate on said interface data of a first data type.
 7. Theintelligent device of any one of claims 1 to 6, operable to ignoredetected data of a second data type that were generated by a source thatwas recorded in memory as a source of data of a first data type in instep a).
 8. The intelligent device of any one of claims 1 to 7, operableto use said interface to generate data of a first data type and whereinthe data of a first data type include a counter, wherein step a) furtherincludes identifying the value of the counter of any data of a firstdata type detected, associate the value of the counter with the recordedidentity information for the source of the data of a first data type,increment the value of the counter and allocate the incremented value toa counter in any data of the first data type generated by theintelligent device as a result of data received from the source of thedata of a first data type.
 9. The intelligent device of claim 8,operable to ignore detected data of a first data type that has a countervalue more than a threshold value.
 10. The intelligent device of claim9, wherein the threshold value is a value related to the value of thecounter from the last data of a first data type received.
 11. Theintelligent device of claim 10, wherein the threshold value is one morethan the value of the counter from the last data of a first data typereceived.
 12. The intelligent device of any one of claims 1 to 11,wherein the data of a third data type include a counter and the datagenerated in step c) is in the form of data of a third data type and theintelligent device associates the value of the counter with theinformation recorded in step c) that identifies the source of the dataof a third data type and the intelligent device increments the counterwhen generating data of a third data type in response to detection ofdata of a third data type in step c).
 13. The intelligent device of anyone of claims 1 to 12, operable to also generate data onto saidinterface otherwise than in accordance with the configuration process.14. The intelligent device of any one of claims 1 to 12, operable togenerate text messages onto said interface.
 15. The intelligent deviceof any one of claims 1 to 12, operable to receive control messagesthrough said interface and communicate control messages to a powerdistribution board to facilitate load shed dependent on said controlmessages.
 16. A power line communication system (100) including aplurality of power lines (7 a-c) in communication with a controller (3)through a power line modem (6), each power line having a plurality ofintelligent devices as claimed in claim 1 in communication with it,wherein the controller (3) is operable as one of said plurality ofintelligent devices (9) and is also in communication with a computercontroller (2) that is operable to receive data from the intelligentdevices (9) via the controller (3) and to send data to the intelligentdevices (9) via the controller (3).
 17. The power line communicationsystem of claim 16, wherein data other than configuration data, which isgenerated onto a power line by an intelligent device or the controller,includes a destination address and an intermediate address, wherein eachintelligent device monitors communications on the power line and if thedestination address of communications matches information identifyingthe source of the data of a second data type (IHY packets) included inthe data of a third data type (IHT packets) that was recorded by anintelligent device in accordance with step c), then that intelligentdevice regenerates the data, but with the intermediate address fieldcomprising the information identifying the source of the data of a thirddata type (IHT packets) recorded in step c) that is associated with theinformation identifying the source of the data of a second data type(IHY packets) included in the data of a third data type (IHT packets)that matches the destination address.
 18. A power line communicationsystem (100) including a plurality of intelligent devices (9) incommunication with a power line and operable to monitor energy usage ata site and communicate usage data onto the power line, and a controller(3) also in communication with the power line, wherein each intelligentdevice (9) maintains a routing table identifying a first set of otherintelligent devices (9) downstream of it relative to the controller (3)that it can communicate with directly and identifying a second set ofother intelligent devices (9) downstream of it relative to thecontroller (3) that it can communicate with through one or more of thefirst set of other intelligent devices (9).
 19. The power linecommunication system of claim 18, wherein the routing table furtheridentifies a third set of other intelligent devices upstream of itrelative to the controller that it can communicate with directly. 20.The power line communication system of 18 or claim 19, wherein therouting tables are formed by an interrogation process initiated by thecontroller that requests the intelligent devices that can receive datadirectly from the controller over the power line to respond withinformation identifying what other intelligent devices the intelligentdevices that can receive data directly from the controller over thepower line can communicate with either directly or through furtherintelligent devices, wherein the intelligent devices that can becommunicated with through said further intelligent devices areidentified through an interrogation process conducted by said furtherintelligent devices.